I've seen the example to list all groups where the Type equals Microsoft365('Unified')
https://graph.microsoft.com/v1.0/groups?$filter=groupTypes/any(c:c+eq+'Unified')
Also another page states ne (not equal) is valid. However I didn't find a way to create a query which gets all Groups where the type is not Unified. I feel the documentation doesn't make quite clear how the /any(c:c [...]) works.
I tried (see below) which don't seem to be supported.
https://graph.microsoft.com/v1.0/groups?$filter=groupTypes/any(c:c+ne+'Unified')
https://graph.microsoft.com/v1.0/groups?$filter=groupTypes/all(c:c+ne+'Unified')